Can I replace main run rigid pipe with hose?
No. The main run and branches must be rigid copper, properly fixed.
Hose may be run between a rigid pipe (fixed) and an appliance, BUT only if the appliance instructions allow it, and if it is a short as practicable, and if it accessible for inspection.
A hose can be run from the rigid pipe of the “vehicle” to the rigid pipe of the “slide out”.
Remember all hose locations needs to be stated in your handover manual. See Clause 5.2.5.